1. Field of the Invention
The present invention relates a method for forming a semiconductor structure having at least a metal connection, and more particularly, to a method for forming a semiconductor structure having a gate and a first contact plug, wherein a top surface of the first contact plug is higher than a top surface of the gate.
2. Description of the Prior Art
Poly-silicon is conventionally used as a gate electrode in semiconductor devices, such as the metal-oxide-semiconductor (MOS). However, with a trend toward scaling down the size of semiconductor devices, the conventional poly-silicon gate has faced problems such as inferior performance due to boron penetration and unavoidable depletion effect which increases equivalent thickness of the gate dielectric layer, reduces gate capacitance, and worsens a driving force of the devices. Therefore, work function metals are used to replace the conventional poly-silicon gate to be the control electrode that are suitable for use as the high-k gate dielectric layer.
In addition, in conventional arts, after forming the transistor with a metal gate, a wiring system is formed thereabove to electrically connect the metal gate and the source/drain, thereby providing a signal input/output pathway for the transistor. However, the wiring system connecting the source/drain in conventional arts usually includes a plurality of contacts plugs, resulting in a problem of high resistance and low electrical performance. Furthermore, as the miniaturization of the devices, a problem of electrical short between the metal gate and the contact plug connecting the source/drain is easy to occur and the quality of the device is decreased as well. Consequently, there is still a need for a novel semiconductor structure having at least a contact plug to resolve the above-mentioned problem.